Dry-etching processes using plasma have been often employed in semiconductor device manufacturing processes. In conventional dry-etching processes, in many cases, etching is performed until the layer to be etched is completely eliminated. However, in some cases, there is a need for terminating etching at the time the depth of a trench being formed by etching reaches a desired depth or at the time the remaining thickness of a layer being etched reaches a desired thickness. In such cases, it is necessary to detect the etching end point with higher accuracy in comparison with usual dry-etching processes.
As a method for accurately detecting an etching end point, there has been known a method which irradiates the surface of a semiconductor wafer with light during etching and detects the etching end point on the basis of the intensity of reflected light from the surface, as disclosed in Japanese Patent Application Laid-Open No. 2001-210619.
The method disclosed in Japanese Patent Application Laid-Open No. 2001-210619 employs, during etching for forming trenches for isolation in a silicon substrate, light containing a polarized light component parallel to the extending direction of parallel mask patterns for the formation of trenches (line-and-space patterns), to thereby improve the accuracy of the end-point detection. Further, there have been suggested various types of etching end-point detecting methods as disclosed in Japanese Patent Application Laid-Open Nos. 8-125283, 9-283585, 11-260799, 2003-229414, 2001-85388 and the like.